FRIDAY, Aug. 27 (HealthDay News) -- Prescription medicines are the way that many drug addicts first get hooked, making these legal medicines the new "gateway" drugs, new study findings show.

University at Buffalo researchers interviewed 75 patients hospitalized for opioid detoxification and found that 31 of them said they first became addicted to legitimately prescribed painkillers.

Another 24 patients said their addiction began when they used a friend's left-over prescription pills or stole drugs from a parent's medicine cabinet, while the remaining 20 patients said they got hooked on street drugs.

But the study found that 92% of the patients said they eventually bought illegal drugs (usually heroin) because street drugs are less expensive and more effective than prescription drugs. Their reasons for continuing to use drugs included to feel "normal," to feel "like a better person" or to ease emotional pain and stress.

"We are seeing an increase in the number of patients addicted to prescription drugs, so we wanted to better understand how they first got hooked," study senior author Dr. Richard Blondell, a professor of family medicine, said in a University at Buffalo news release.

"This information suggests that there is a progressive nature to opioid use, and that prescription opioids can be the gateway to illicit drug addiction. It also tells us that people who use prescriptions illegally may be at greater risk for subsequent heroin use than those who use prescriptions legally."

The study was published recently in the Journal of Addiction Medicine.